Effects of daytime carbon dioxide concentration on dark respiration in rice

Rising atmospheric carbon dioxide concentration (CO₂]) has generated considerable interest in the response of agricultural crops to CO₂]. The objectives of this study were to determine the effects of a wide range of daytime CO₂] on dark respiration of rice (Oryza sativa L. cv. IR-30). Rice plants were grown season-long in naturally sunlit plant growth chambers in subambient (160 and 250), ambient (330), or super-ambient (500, 660 and 900 μmol CO₂ mol^?1 air) CO₂] treatments. Canopy dark respiration, expressed on a ground area basis (R_d) increased with increasing CO₂] treatment from 160 to 500 μmol mol^?1 treatments and was very similar among the superambient treatments. The trends in R_d over time and in response to increasing daytime CO₂] treatment were associated with and similar to trends previously described for photosynthesis. Specific respiration rate (R_dw) decreased with time during the growing season and was higher in the subambient than the ambient and superambient CO₂] treatments. This greater R_dw in the subambient CO₂] treatments was attributed to a higher specific maintenance respiration rate and was associated with higher plant tissue nitrogen concentration.